Restricted key system

ABSTRACT

A restricted key system providing keys/key slots with an angled or chevron shaped cross sectional profile. Each key blade of the restricted key system includes an upper planar portion which is bitted or cut to position the standard pin tumblers, an intermediate portion which forms a horizontal ledge, and a lower planar portion which extends from the intermediate portion at an angle in the range of 5°-85° relative to the upper planar portion. The horizontal ledge of the key blade may be provided with at least two additional bitting surfaces for wards, tumblers and/or other key differing elements.

BACKGROUND OF THE INVENTION

My invention relates to improvements in keys and key barrels forconventional lock cylinders and cylinders which have key-removablecores. Such well known mechanisms use pin tumblers which are evenlyspaced in a single row along the length of the key barrel. Inparticularly, my invention relates to keys having new cross-sectionalprofiles and the corresponding key barrels suitable for such keys.

In general, my invention relates to conventional key cylinders andcylinders which use key-removable cores of the type described in U.S.Pat. No. 2,814,941 (Best), U.S. Pat. No. 3,603,123 (Best), and in G. L.Finch's Service Manual entitled "Servicing Interchangeable Cores,"revised in 1988.

The above-noted key-removable, interchangeable cores have been inwidespread use in the United States for more than 20 years. Suchinterchangeable cores permit unskilled persons to rekey locks (i.e.,block-out existing keys) in 10 to 15 seconds without opening the door orremoving the cylinder body. To achieve the convenience ofinterchangeable cores, all interchangeable cores in a given system arepinned for release from their housings by a single "control key." Thecontrol key is actually a "top" master key whose sole function islimited (15 degree rotation) to operation of the blocking lug whichretains the core in the cylinder body. Control keys are not visuallydistinguishable from other keys in the system. Typically, the core isalso pinned to one or more master keys and to a tenant key. Such asystem usually requires three or four pin segments in each pin column,an arrangement which offers very limited pick-resistance.

In large institutions such as colleges, hospitals, etc., door locksecurity is threatened by the circulation of unauthorized keys. Inrelative terms, lock-picking is a minor consideration. While a buildingmanager's ability to instantly rekey with interchangeable cores clearlypromises a degree of key control, a serious problem exists inuniversities, for instance, where students can have unauthorized copiesof their keys made at a hardware store or lockshop. The most practicalprotection against this security compromise resides in proprietary keys(patented) which only can be made and duplicated by the lock maker or anauthorized locksmith, (a) because key blank distribution is restrictedby the manufacturer, (b) because the key blank cannot be bitted(finished) on machines in current use by keymakers and locksmiths. Anadditional level of protection exists if prior art key blanks cannoteasily be modified or counterfeited to enter proprietary key slots and,when proprietary key blanks cannot be bitted in a single operation on asingle machine. Further, although not generally known, master keyingtechnology, similar to that employed in generic interchangeable cores,may reduce the number of usable change keys in a single system tobetween 2 and 5% of those available in non-master keyed cylinders. Sucha limited number of key changes may not be enough to guaranteetrustworthy locks in a medium-sized institution. Accordingly, when toofew key changes are available, there is no certainty that a key to onelock will not inadvertently operate other locks on the premises.

Key removable, interchangeable cores are manufactured by most Americanlockmakers. Core interchangeability is usually limited to the housingsof a single manufacturer (i.e., SARGENT cores in SARGENT housings, YALEcores in YALE housings, etc.). However, the interchangeable coresreferenced in the above-noted Finch's Service Manual are generic in thesense that a BEST core fits (i.e., interchanges with) the housings ofARROW, FALCON, EAGLE and others. Likewise, the cores of ARROW, FALCON,EAGLE and others fit the BEST housings, etc. without onsitemodification.

Further exacerbating key control problems is the fact that theabove-mentioned generic cores all use common, warded key slots which aresuited to flat keys which are grooved on both sides. 100,000 groovepatterns are in the public domain. Some milling differs are so minutewhen compared with each other, that they cannot perform their securityfunction as intended, particularly when the key slots are worn or werenot broached to close tolerances.

Typical keys for generic cores are milled on two flat surfaces. The keyslot warding reflects the milling pattern of the lowest level keys(i.e., the keys assigned to tenants). Master keys are thinner sectionswhich are side milled to enter (pass) selected groups of key slots. Thetop master key and the control key must enter all key slots in a givensystem, which may number in the thousands.

Typical hierarchical order of keys/sections:

CONTROL KEY will change all cores in a system.

GRAND MASTER KEY will unlock any lock in the system.

MASTER & SUBMASTER KEYS unlock only specific groups of locks.

TENANT KEYS unlock one lock only. In large systems tenant keys arebitted on several related (family) key sections under each master key.

Control and Grandmaster Keys may be bitted on the same key blanksection. Master key blank sections (because they must pass two or morekey slots that differ) are usually thinner sections.

However, in practice, problems arise in such systems since blankmanufacturers do not restrict the distribution of key blanks used to bitor cut the keys for the generic cores. Further, hardware stores and somekeymakers only stock master key blank sections, which of course willenter all cores in a group. Some will enter all cores in the system.Some will enter cores in every generic core system.

Thus, there are tens of millions of generic interchangeable cores ondoors throughout America. Statistically, even the lowest level keys(i.e., tenant keys) can be expected to unintentionally operate thousandsof interchangeable cores in systems other than their own.

In addition, since biting combinations for master keys are randomlyselected, a tenant key from almost any generic core system, when copiedon a control key blank section, has the potential of operating cores, orremoving cores from their housings in other systems across the street oracross the country.

U.S. Pat. No. 2,049,548 (Swanson) discloses a guard tumbler which iscomprised of two members which are biased toward the key slot by acompression spring. The guard is similar in construction to that ofconventional pin tumblers except that it is longer than the othertumblers and its operating chamber extends to the bottom of the keyslot, as shown in FIG. 1. In order to effect release of the key barrel,a key having a notched lip and a supporting wing is employed. The lip isprovided with the usual notches (bittings) for positioning the tumblersand a guard releasing notch is formed in the inner end of the lip,between the lip and the key bow. Because of the employment of a guardreleasing notch, the supporting wing is included to obtain sufficientstrength in the key. FIGS. 10 and 11 of Swanson show variations on theform of the angularly shaped key slot for receiving a like shaped keyblade. Thus, the portion of the key blade which corresponds to the lowerportion of the key slot in FIG. 10 and which corresponds to thehorizontal portion of the key slot in FIG. 11 serve the same purpose asthe supporting wing of the first embodiment.

However, FIGS. 10 and 11 both show angular keys (dotted lines and seeclaim 7) which are notched forward of the bow for the guard tumbler.This leaves only 4 tumbler positions on the key which can be bitteddifferently. 10 bitting increments to the 4th power can yield a maximumof 10,000 theoretical key changes; not near enough for contemporaryrequirements.

The key in FIG. 10 has parallel legs of the same width. This permits keyduplication on conventional bitting machines. The skewed key slot,however, precludes placing secondary wards or tumblers directly beneaththe horizontal leg of the key in line with the primary tumblers.

The key in FIG. 11 has right angle legs of the same width. The keycannot lay flat, an important consideration for consumer acceptance inthe 1990's.

U.S. Pat. No. 4,683,740 (Errani) is similar to Swanson. In particular,upon inserting a picking tool (see FIG. 3) in an attempt to bring thepins to shear at the key barrel periphery, one or more pins areunavoidably extended into the cylinder body, thus inhibiting key barrelrotation.

However, the Errani key's horizontal portion separating a bittingportion from a support portion is uniquely undercut to compliment arestricted-access key slot. The secondary key differing elements arebitted on both sides of the support portion. All blade portions relativeto the key bow are on a single plane. The restricted access key slotrequires a key with a much wider support portion than usual whichgreatly limits the number of key changes that can be generated by theremaining relatively shallow bitting portion which positions the primarytumblers. Errani's horizontal portion cannot be bitted on its underside.

U.S. Pat. No. 4,416,128 (Steinbrink) relates to an arcuate skeleton in aflat key to resist the effectiveness of a pick-gun.

U.S. Pat. No. 2,814,941 (Best), U.S. Pat. No. 3,603,123 (Best) and U.S.Pat. No. 4,294,093 (Best) each relate to key-removable lock coresemploying the standard key slot.

SUMMARY OF THE INVENTION

It is an object of the present invention to correct the above-mentionedproblems/deficiencies by providing keys/key slots with new crosssectional profiles which, for instance, are readily produced from flatmetal stampings.

It is a further object of the present invention to create a proprietaryrestricted key system capable of generating an extraordinary number ofchange key combinations which were heretofore unavailable.

It is a further object of the present invention to create aseries/family of proprietary key slots which block entry to all priorart keys.

It is a still further object to create a series/family of proprietarykey sections which cannot be bitted (i.e., cut) on machines currentlyused by locksmiths and commercial key copiers.

It is yet another object of the present invention to create proprietarykey sections and corresponding key slots for interchangeable cores whichcan also be used in conventional key cylinders.

It is a further object to make these improvements without materiallyaltering the well-known construction of conventional key cylinders andgeneric key-removable cores.

To enhance the pick-resistance of key cylinders by restricting freeaccess to the pin columns and torquing means.

To enhance the security of key cylinders by making it impractical tocounterfeit keys.

To enhance key control by making it impractical to make unauthorizedcopies of keys.

To enhance drill-resistance by placing carbide pins directly underselected pin columns.

These objects are achieved by the present restricted key system which isintended to operate proprietary cores in state of the art generic corehousings. Central to the present restricted key system are a family ofangled key sections which lend themselves to the usual wardingtechniques, new key section differing methods and new secondarybittings.

The restricted key system provides key/key slots with an angled orchevron shaped cross sectional profile. Each key blade of the restrictedkey system includes an upper planar portion which is bitted or cut toposition the standard pin tumblers, an intermediate portion which formsa horizontal ledge, and a lower planar portion which extends from theintermediate portion at an angle in the range of 5°-85° relative to theupper planar portion. The horizontal ledge of the key blade may beprovided with at least two additional bitting surfaces for wards,tumblers and/or other key differing elements.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will be apparentfrom the following description taken in connection with the accompanyingdrawings wherein:

FIG. 1 is an exploded view of a key operated, interchangeable coresubassembly according to the present invention;

FIG. 2 is a front end view of the core subassembly showing the key slotaccording to the present invention;

FIG. 3 illustrates key bitting details and shows lower limits of pinchambers where they intersect with smaller diameter core service holes.

FIG. 4 is an enlarged cross sectional view of the key blade according tothe present invention taken along the lines, 4A--4A in FIG. 3;

FIG. 5 is a side view of the key according to a second embodimentwherein a secondary bitting surface is provided under a horizontal ledgeportion;

FIG. 6 is an enlarged cross sectional view of the key blade of FIG. 5taken along the lines .[.6A--6A.]. .Iadd.6--6.Iaddend., with a secondaryward pin or tumbler being shown;

FIG. 6A is a partial cross sectional view showing a carbide warding pinengaging a groove in the key blade;

FIG. 7 is a side view of the key according to a third embodiment whereina secondary bitting surface is provided along a corner of the horizontalportion of the key blade;

FIG. 8 is an enlarged cross sectional view of the key blade of FIG. 7taken along the lines 8A--8A, with a secondary ward pin or tumbler beingshown; and

FIG. 9 is a perspective view of a standard key cylinder utilizing theinventive key slot and key.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will now be described with reference to the drawings. Asshown in FIG. 1, a key operated, interchangeable core subassembly 1 ofthe present restricted key system is shown exploded for ease ofdescription. The core subassembly 1 is fitted into a like-shaped openingin a cylinder body or housing (not shown) which remains in the door orthe like. The core subassembly 1 includes an outer shell 2 having afigure-8 shaped cross section. The outer shell 2 has a plurality ofvertical bores or pin chambers 3 for receiving pin stacks S (describedlater). At the lower portion of the outer shell 2, core service holes 8,through which a tool is introduced to forcibly remove tumblers from thecore subassembly prior to rekeying, are disposed.

A sleeve 9 having a blocking or locking lug 9' formed thereon is fittedwithin a cylindrical bore C formed in the lower portion of the outershell 2 from the rear. The sleeve 9 has upper bores 10 which correspondto the bores 3 of the outer shell 2. The lower holes 11 are serviceholes which correspond to holes 8.

A rotatable key barrel 12 is inserted at the front of the outer shell 2and is fitted within the sleeve 9. The key barrel 12 includes aplurality of bores 13 on a radial plane and which correspond to thebores 10 of the sleeve 9 and the bores 3 of the outer shell 2. The bores13 extend into the key barrel 12. The key barrel 12 has a key slot 19which extends longitudinally in the key barrel for receiving a key andintersecting the bores 13. A dimple D is drilled in the key barrel faceto facilitate smooth key entry. The key barrel 12 also includes a pairof posts 14 and 15 to which a key stop disc 16 is mounted. The key stopalso retains the key barrel in the subassembly.

The pin stacks include bottom pins 4 which are radially adjusted withinthe bores 13 by corresponding bittings cut in the top edge of the key.Above the bottom pins 4 lie the master pins 5. The master pins create asecond shear line for a master key. Next, the control pins 6 aredisposed above the master pins 5. The control pins 6 create a controlshear line for a control key. Finally, the top pins 7, called drivers,are the uppermost pins in the pin stacks. Cylinder springs 17 rest ontop of the pin stacks and apply a downward compression force to thestacks. Cylinder caps 18 are used to close the chambers of the core.

Therefore, the initial function of a control key is to align thedivisions between the top pins 7 and the control pins 6 at the outerperiphery of the control sleeve 9, and position one or more pin segmentsto block independent rotation of the key barrel 12. The control sleeve 9and the key barrel 12 rotate in unison. Turning the control keyclockwise 15 degrees or so retracts the blocking lug 9', permittingwithdrawal of the core subassembly 1.

The control key cannot be withdrawn from the core unless the blockinglug 9' is in the extended (blocking) position.

Inserting a new core 1 requires retracting the blocking lug 9' with acontrol key, inserting the core subassembly in the figure-eight housing,and turning the control key (key barrel/control sleeve)counterclockwise. Removal of the control key confirms that the operationis complete. The expired time is 15 to 20 seconds for this operation.

Similarly, the initial function of master and tenant keys is to alignthe divisions between selected pin segments to coincide at the keybarrel periphery. The key barrel 12 interfaces with connecting elements(not shown) which extend or withdraw a lock bolt (not shown) as the keyturns.

In generic key interchangeable cores, two longitudinal blind cavitiesbored parallel to the key slot from the back end of the key barrelengage corresponding prongs (not shown) which are rotatably disposed inthe core housing to operate the bolt mechanism as the key turns.

The cutout on the bottom of the key tip has long been associated withinterchangeable cores. Stopping key entry at the tip instead of at thebow shoulder permits a single key blank to be used for 5, 6, or 7 pinmechanisms. The dimensional obstacles imposed by the key stop plateconnecting means (posts) and the prong cavity locations have discouragedkey section design variations except for the usual milling/wardingtechniques.

The detailed description so far of the interchangeable core subassembly1 is well known to those skilled in the art. A further disclosure of theoperation of a pin tumbler type lock can be found in U.S. Pat. No.3,603,123 (Best), which disclosure is incorporated herein by reference.

As shown in FIGS. 1 and 2, the key slot 19 (and key blade 21 of the key20) of the present restricted key system have an angled key section 22which allows for the usual side milling/warding techniques, new keysection differing methods and new secondary bittings. While both the keyblade 21 and the key slot 19 have the inventive angled shape, the key 20will now be described in detail.

In general, the key 20 includes a bow member 23 which is adapted to begrasped by the fingers of a user, and a key blade 21 which enters thekey slot 19. The key blade is functionally divided horizontally. Theupper portion of the key is cut or bitted to position primary tumblersof varying lengths (see FIG. 3). The intermediate and lower portionssupport the upper bitting portion and have secondary functions of theirown.

As best seen in FIG. 4, each key blade 21 of the present restricted keysystem has an angled or chevron shaped cross section. The uppervertical, planar portion 24 is bitted to position the standard pintumblers P, one of which is shown in phantom lines. Of course, there isa plurality of pin stacks as shown in FIG. 1.

An intermediate portion 25 forms a horizontal ledge 26. As will bediscussed in more detail below, the horizontal ledge 26 serves twoprimary functions. First, it provides reference and support in keymaking operations, and second, it provides at least two additional,(optional) bitting surfaces for wards, tumblers and/or other keydiffering elements.

A lower planar portion 27 extends at a predetermined angle α from theintermediate portion 25. The angle α can be set in the range ofapproximately 5°-85° with respect to a vertical line extending downwardfrom the point where the horizontal ledge 26 meets the inner face 28 ofthe lower planar portion 27.

The practical range of angles for key sections is limited by the fixedlocation of prong cavities G (see FIGS. 4 and 8) and the mounting postsfor the key stop. It is the common location of the prong cavities, theirlength and diameter which permit all cores in the generic group to beinterchangeable. The cavity locations may be the primary reason thatBEST and others have focused on proprietary pinning systems to generateadditional key changes. Best (U.S. Pat. No. 3,603,123) Table 1, relieson base 7 bitting increments to increase the usable key combinations in6 tumbler cores, from the traditional 4,096 changes to 46,656. This isachieved by reducing incremental bitting depths from 0.025" to 0.018".The 0.007" trade-off for additional key changes lessens the cylinder'sresistance to key jiggling and interchange.

The present invention generates an extraordinary number of theoreticalkey changes by using two additional key bitting surfaces. The elementspositioned by the new bittings inherently resist key jiggling techniquesas well as inadvertent key interchange; both serious problems associatedwith generic key-removable cores.

A key with an angle α of 15° for instance, can be readily andeconomically machined from sheet metal stampings with a minimum ofmaterial waste (scrap).

The angled key blade cross section of the present invention presentsinnumerable new key blank differing possibilities that cannot begenerated by the usual milling/warding techniques. In particular, therestricted key system cross section provides nine profile surfaces Athrough I compared with four surfaces in prior art keys. At least fiveof the nine profile surfaces lend themselves to two differingtechniques. In particular, surfaces B, D, E, G and I are variable. Thefirst differing technique is that each of the surfaces B, D, E, G and Ican be milled to pass a corresponding ward in the key slot 19. Thiscreates two differs (i.e., milled or unmilled). The second differingtechnique is that the five surfaces B, D, E, G and I can be madeslightly thicker, or independently shifted up, down, right or left of acommon center or default position to create two additional differs(shifted/unshifted). Thus, four variable applied to five surfaces yield1024 discrete key blank sections for each incremental blade anglevariation. Note, this number may be doubled for conventional lockcylinders (without interchangeable cores) or interchangeable cores whichuse a different key stop method, that can use mirror image key sectionsextending into the opposite, or left side of the key barrel.

More importantly, the angled change keys/blanks of the presentrestricted key system will enter no key slot but their own. Likewise,the series/family of proprietary key slots will block entry to all priorart keys.

The key blanks/sections of the present invention can be drawn, cast orstamped from sheet metal and customized by well-known mass productiontechniques. The key blank thickness and profile of the present inventioncannot be readily procured through normal distribution channels. Thespecific widths of the stamping required to produce angled key blankswith a varying angle α are as follows:

    ______________________________________                                                    Unmilled Key                                                      Angle α                                                                             Blank Thickness                                                   ______________________________________                                        15°  .120"                                                             25°  .136"                                                             30°  .139"                                                             45°  .150"                                                             ______________________________________                                    

The chart illustrates a limited selection of angled key sections to showsome practical variations, but those skilled in the art will recognizethat variations of 5 degrees are sufficient to prevent keys of anystandardized angle from entering key slots formed at anotherstandardized angle.

The key blade 21 and key bow 23 can be stamped and machined in onepiece. The bow 23 can be in alignment with the upper planar portion 24of the key blade 21 having the standard bitting thereon or aligned withthe lower planar portion 27 of the key blade 21. Alternatively, the keyblade 21 can be stamped and machined without a bow. A separate handlepiece can then be affixed substantially in line with the upper planarportion 24 of the key blade 21 or in line with the lower planar portion27 of the key blade 21.

As noted above, the horizontal ledge 26 of the key blade 21 provides atleast two additional, optional bitting surfaces. The embodiment of FIGS.5 and 6 illustrates a bitting surface 29 provided directly under andalong the horizontal ledge 26 of the key blade 21 (note, like referencenumerals are used to denote like elements). The bitting surface 29 is inaddition to the normal bitting surface disposed along the upper portion24. Binary tumbler bittings under the horizontal ledge are dimples 29'which are approximately 0.020" deep. Logically, drilled dimples wouldnot appear in all bitting positions.

A secondary tumbler 30 illustrated in FIG. 6 operates in the serviceholes. The binary tumbler tip portion which engages the bitting ispointed to match the shape of the dimple 29'. It's other ends is roundedto seat in the service hole in the blocking lug sleeve. If the key hasproperly positioned the primary tumblers, attempts to rotate the keybarrel 12 will cam the binary tumblers towards the horizontal ledge 26in the key. If the key is unbitted where a bitting is required, therounded end of the tumbler cannot disengage from the non-rotatablesleeve, preventing key barrel rotation.

As shown in FIG. 6A, when the underside of the horizontal ledge 26 isoptionally used to restrict key entry, a carbide warding pin 30' isplaced in a specific service hole to block entry of keys which are notgrooved from key tip to the pin position. For example, one group oftenant keys would be grooved to pass a ward pin in the No. 3 position,for instance. Tenant keys in another group would be grooved to pass award pin in the 4th position, etc. The top master key and control keywould be grooved the length of the key blade to pass all ward pins.

The depth of the groove 31 and the depth of any individual secondarybittings would be approximately 0.015-0.020". When only some pinpositions are warded for key blocking purposes, portions of the bladenot grooved can optionally be bitted for secondary tumblers.

In a third embodiment, as shown in FIGS. 7 and 8, a still furtherbitting surface 35 may be provided in addition to or in lieu of theadditional bitting surface 29, as shown in FIG. 6. The bitting surface35 is provided along a corner portion 36 formed where the horizontalledge 26 meets an outer surface 37 of the upper planar portion 24 of thekey blade 21. As shown in FIG. 8, a second set of spring/tumblercavities can optionally be bored to the left of the key slot 19. Note, asingle pin P' and bore B' are visible in FIG. 8. If six secondarytumblers with binary differs are disposed along the corner of thehorizontal ledge 26, this would multiply the present theoretical keychange potential from 1,000,000 (primary tumblers) to 64,000,000 changesper discrete key blank section.

In common pin tumbler cylinders, and cylinders with key removablegeneric cores, the tumblers are evenly spaced in a single row along thelength of the key barrel. Key differing is a theoretical process whichdivides the bitting portion of the key blade horizontally into standarddepth increments.

A key bitting blade which is 0.150" wide, can for instance, generate tenbitting depth increments of 0.015" each. In a 6 tumbler system,1,000,000 theoretical keys can be made which differ from each other by aminimum depth variation of 0.015" in at least one bitting position. Suchincrements are too minute to be reliable mechanically. Double incrementsof 0.030" are widely accepted as being more practical.

5 incremental differs of 0.030" each offer more realistic protectionagainst key interchange. In the same system, they will yield only 15.625theoretical key bitting combinations.

The 15.625 theoretical key differs above are reduced to a maximum of4,096 change key bitting combinations when a 0.030" pin segment isplaced between top and bottom pins in each pin column for masterkeying.

The present invention increases the theoretical key change potential ofgeneric pin tumbler mechanisms from 1,000,000 to 4,096,000,000 bittingcombinations per discrete key section, as follows:

1,000,000 theoretical changes attributed to six primary tumblers above.

    ______________________________________                                        64          theoretical changes attributed to                                             six binary secondary bittings under                                           the horizontal ledge. 2 to the 6th                                            power.                                                            64          theoretical changes attributed to                                             six binary secondary bittings on the                                          corner of the horizontal ledge. 2 to                                          the 6th power.                                                    64 × 64 = 4,096 × 1,000,000 = 4,096,000.                          1,024       Discrete key sections based on shifted/                                       unshifted and milled/unmilled options.                            9           Key section angle options in the range of                                     5 to 45 degrees.                                                  1,024 × 9 = 9,216                                                                   Proprietary key blank sections.                                   17          Key section angle options in the range of                                     5 to 85 degrees.                                                  1,024 × 17 = 17,408                                                                 Proprietary key blank sections.                                   4,096,000,000                                                                             Theoretical key changes for each of                               17,408      Proprietary key blank sections.                                   ______________________________________                                    

Since the key blanks of the present restricted key system do notresemble the prior art keys, the key blanks will not fit conventionalkey machines. In particular, an attempt to duplicate a restricted keysystem key would disclose (a) the lower angled leg of the key blank, ifone were available, cannot be independently supported by key machinevises in current use; (b) even if the blank is supported at the bow, theconventional cutter would produce primary bittings which are high on oneside and would have to be finished by hand. In addition, the secondarybittings and/or grooves require two additional machine set ups and this,in turn, makes key counterfeiting more complicated and impractical.

The present restricted key system is equally applicable to a standardkey cylinder 40 (see FIG. 9) wherein the core is not key removable. Ofcourse, it would be necessary to bore holes for the carbide pins, etc.to be conveniently disposed longitudinally under the horizontal ledge 26since there are no existing service holes as in the removable core typecylinder.

With the above-described restricted key system, the following advantagesare realized:

SECURE KEY CHANGES: Additional bitting increments permit the factory todiscard well known key bitting combinations that are likely to operatemore locks in a given system than intended.

INCREASED PICK RESISTANCE: In particular, in prior art cores a comb-likepicking tool inserted in the keyslot can engage and apply the necessarytorque to the blocking lug sleeve. In the present invention, the angled,offset key slot blocks direct access to the service holes. In addition,new, safe bitting combinations permit the factory to disregard bittingcombinations that are relatively easy to pick.

INCREASED DRILL-RESISTANCE: Carbide pins are inserted in one or morecore service holes to stop or misdirect drill bits.

ENHANCED KEY CONTROL: Proprietary key and key blank distribution iscontrolled at the factory. An extraordinary number of unique keysections and key bitting combinations greatly reduces the probability ofany key operating the wrong lock. Two dissimilar key bitting techniquesand the unavailability of machines for the duplication of the presentrestricted key system restores building management control overunauthorized key duplication.

It is contemplated that numerous modifications may be made to therestricted key system of the present invention without departing fromthe spirit and scope of the invention as defined in the followingclaims.

What is claimed is:
 1. A key blank comprising:a) a bow member adapted tobe grasped by fingers of a user, and b) an elongate blade extendingoutwardly from the bow member and defining, in transverse crosssection,an upper planar blade portion extending inwardly from onelongitudinal edge of the blade, and a lower planar blade portionextending inwardly from another, opposite longitudinal edge of the bladeand adjoining an innermost edge of the upper blade portion in anintermediate .Iadd.ledge .Iaddend.portion of the blade, c) wherein:theplane of the upper blade portion is oriented at a predetermined angle,in a range of 5° to 85° relative to the plane of the lower blade portionto define a general chevron shape therewith.
 2. The key blank accordingto claim 1, wherein said upper planar portion includes a bitting surfacealong said one longitudinally edge of said blade.
 3. The key blankaccording to claim 1, wherein said intermediate .Iadd.ledge.Iaddend.portion includes a horizontal ledge, said horizontal ledgehaving a bitting surface disposed directly under and along saidhorizontal ledge of said blade.
 4. The key blank according to claim 2,wherein said intermediate .Iadd.ledge .Iaddend.portion includes ahorizontal ledge; and further comprising an additional bitting surfacedisposed directly under and along said horizontal ledge of said blade.5. The key blank according to claim 1, wherein said intermediate.Iadd.ledge .Iaddend.portion includes a horizontal ledge, saidhorizontal ledge meeting an outer surface of said upper planar portionat a corner portion; and further comprising a bitting surface disposedalong said corner portion.
 6. The key blank according to claim 2,wherein said intermediate .Iadd.ledge .Iaddend.portion includes ahorizontal ledge, said horizontal ledge meeting an outer surface of saidupper planar portion at a corner portion; and further comprising anadditional bitting surface disposed along said corner portion.
 7. Thekey blank according to claim 1, wherein said predetermined angle is in arange of 15° to 45°.
 8. A cylinder lock comprising:a lock cylinderhaving a cylindrical bore formed therein; a key barrel rotatably mountedwithin said cylindrical bore; a first set of bores formed in said keybarrel on a radial plane; a plurality of pins slidably disposed in saidfirst set of bores; a key slot extending longitudinally in said keybarrel for receiving a key and intersecting said first set of bores; asecond set of bores formed in said lock cylinder; and a plurality oftumbler pins slidably disposed in said second set of bores; wherein saidkey includes an elongate blade defining in cross section: an upperplanar blade portion extending inwardly from one longitudinal edge ofthe blade, and a lower planar blade portion extending inwardly fromanother, opposite longitudinal edge of the blade and adjoining aninnermost edge of the upper blade portion in a intermediate .Iadd.ledge.Iaddend.portion of the blade, wherein the plane of the upper bladeportion is oriented at a predetermined angle, in a range of 5° to 85°relative to the plane of the lower blade portion to define a generalchevron shape therewith; and further wherein said key slot is similarlyshaped in cross section so as to receive said blade.
 9. The cylinderlock according to claim 8, wherein said intermediate .Iadd.ledge.Iaddend.portion of said blade includes a horizontal ledge, saidhorizontal ledge having a bitting surface disposed directly under andalong said horizontal ledge of said blade;said lock cylinder furthercomprising an additional set of bores disposed directly under a portionof said key slot opposite to said horizontal ledge, said additional setof bores being filled with carbide pins.
 10. The cylinder lock accordingto claim 8, wherein said lock cylinder includes a key removable coresubassembly, said core subassembly having a figure-8 shaped crosssection and being fitted into a like-shaped opening in said lockcylinder, said cylindrical bore for rotatably mounting said key barrelbeing formed within said core subassembly.
 11. The cylinder lockaccording to claim 8, wherein said intermediate .Iadd.ledge.Iaddend.portion of said blade includes a horizontal ledge, saidhorizontal ledge meeting an outer surface of said upper planar portionat a corner portion, said corner portion having a further bittingsurface formed thereon; said lock cylinder further comprising a furtherset of bores disposed along a portion of said key slot opposite to saidcorner portion of said blade, said further set of bores being filledwith further set of tumbler pins for engaging said further bittingsurface of said blade.
 12. The cylinder lock according to claim 8,wherein said predetermined angle is in a range of 15° to 45°.
 13. Thecylinder lock according to claim 8, wherein said key blade having saidgeneral chevron shape defines nine profile surfaces to attendantlyprovide for additional key blank differing.
 14. A cylinder lockcomprising:a lock cylinder having a cylindrical bore formed therein; akey barrel rotatably mounted within said cylindrical bore; a first setof bores formed in said key barrel on a radial plane; a plurality ofpins slidably disposed in said first set of bores; a key slot extendinglongitudinally in said key barrel for receiving a key and intersectingsaid first set of bores; a second set of bores formed in said lockcylinder; and a plurality of tumbler pins slidably disposed in saidsecond set of bores; wherein said key includes an elongate bladedefining in cross section: an upper planar blade portion extendinginwardly from one longitudinal edge of the blade, and a lower planarblade portion extending inwardly from another opposite longitudinal edgeof the blade and adjoining an innermost edge of the upper blade portionin an intermediate portion of the blade, wherein the plane of the upperblade portion is oriented at a predetermined angle relative to the planeof the lower blade portion to define a general chevron shape therewith;and further wherein said key slot is similarly shaped in cross sectionso as to receive said blade, wherein said intermediate portion of saidblade includes a horizontal ledge, said horizontal ledge having a groovedisposed directly under and extending longitudinally along saidhorizontal ledge of said blade; said lock cylinder further comprising anadditional set of bores disposed directly under a portion of said keyslot opposite to said horizontal ledge, a corresponding one of saidadditional set of bores being filled with a carbide warding pin forregistering with said groove, and further wherein said groove extendsfrom a tip of said blade to such a length so as to allow said key tofully enter said key slot. .Iadd.
 15. A key for a cylinder lock, the keyhaving a bow portion to be grasped by the fingers and a key blade forentering a complementary shaped key slot, the key blade beingfunctionally longitudinally divided horizontally with a planar upperportion bitted on its upper surface to position tumblers in the sameplane as the planar upper portion, and a lower portion extending at anangle of between 5° and 85° relative to the plane of the upper portion,the upper and lower portions being joined at an intermediate horizontalledge portion which includes at least one flat surface for presentingadditional new key differing possibilities and preventing the key fromentering a key slot other than those having a complementary angledshape. .Iaddend..Iadd.
 16. A cylinder lock and key combinationcomprising:a lock cylinder having a cylindrical bore formed thereon, akey barrel rotatably mounted in the cylindrical bore, a set of tumblerpin holes formed in the key barrel on a radial plane, a plurality oftumbler pins slidably disposed in the set of bores, a key slot extendinglongitudinally of the key barrel for receiving a key and intersectingwith the bores, the key slot being configured with an upper slot portionand a lower slot portion, the lower slot portion being oriented at apredetermined angle in the range of 5° to 85° relative to the plane ofthe upper slot portion, and a key having a key blade with an upperplanar portion and a lower planar portion, the angle between the twoplanar portions of the key blade being the same as the angle between thetwo portions of the key slot so that the blade fits into the slot,wherein the upper and lower planar portions are joined by anintermediate horizontal ledge portion, and the upper edge of the upperblade portion is bitted to properly position the tumbler pins in thetumbler pin holes to operate the cylinder lock. .Iaddend.